Radio beacon



y 3, 1951 F. DE FREMERY 2,551,828

RADIO BEACON Filed Feb. 11, 1947 2 Sheets-Sheet l BALANCED ODULATORBALANCED MODULATOR MODULATED IFINAL AMPLIFIER l'I-F AMPLIFIER FREQUENCYMULTIPLIER H-F OSCILLATOR FREQUENCY DOUBLER FREOUENCY MULTIPLIERFREQUENCY MULTIPLIER FREQUENCY I-F AMPLIFIER H-F {IMPLIFIER I M XERWDETECTOID INVENTOR FRANK DE FREMERY Patented May 8, 1951 RADIO BEACONFrank dc Fremery, Eindhoven, Netherlands, as-

signor to Hartford National Bank and lrust Company, Hartford, Conn., astrustee Applicationv February 11, 194-7, Serial No. 7 27,765v In theNetherlands February 5, 1944 Section 1, Public Law 690, August 8, 1946Patent expires February 5, 1964 6 Claims. I

The copending patent application, Serial Number 680,901, filed July 2,1946, now Patent No. 2,530,600, issued Nov. 21, 19.50, discloses amethod of determining the direction of a receiver with respect to abeacon transmitter, by means of the angle ,8 which the direction to bedetermined forms with a known orientation direction, this methodconsisting in that a measuriir characteristic which is a measure for theangle ,8 is derived from the relative position of two oscillationshaving different frequencies a: and no between which a harmonic relationexists and which appear in such a manner that the two oscillations havea phase corresponding with the angle [3.

If n exceeds 2 this method permits the value of the angle ,8 to bedetermined with great delicacy, since a measuring characeristic being afunction of (nil) ,8 can be derived from the relative position of thetwo oscillations w and no.

f, in effect, the two oscillations w and 7m are emitted in such a mannerthat in the direction of orientation the two oscillations w and no passat least once through zero simultaneously at least once per cycle of theoscillation having the lower frequency, two oscillations, one of whichis proportional to sin. (ct-:3) and the other to sin. (mutt/3), areobtained in any direction which forms an angle 5 with the direction oforientation. From these two oscillations the angle [3 to be determinedcan be derived in various ways, for instance by frequency-multiplicationn-times of he oscillation having the lower frequency obtained afterdetection, the result being an oscillation which is proportional to sin.(nwtinfi) By determining the phase angle between thefrequency-multiplied oscillation and the oscillation having the higherfrequency obtained after detection, which is proportional to sin.(nwtis), a measuring characteristic is obtained which is determined by(niDfi, thus obtaining a great measuring accuracy.

However. in the space surrounding the beacon device nil sectors areformed, between which the measured angle (n ne varies in any instancefrom O to 27l' radials, so that the obtained measuring characteristicindicates the possible position of the direction to be determined ineach of these sectors, due to which the spacial angle is not determinedunequivocally by the measuring charecteristic in question. 1

In order to avoid ambiguity of the measuring characteristic in cases,where it may give rise to trouble, a third oscillation having afrequency, which is harmonically related to at least one of theoscillations w and no, is, according to the in (Cl. 3&35-106') vention,transmitted in such a manner as to permit a measuring characteristic,which is an un equivocal measure of the angle [3, to be derived from therelative position of the third oscillation and the oscillation having afrequency w or Ttw which is harmonically related thereto.

The frequency of the third oscillation preferably amounts to half ordouble the frequency ofone of the oscillations w or and the phase of thethird oscillation varies in the same sense with the direction as thephase of the said oscillation w or flu.

In another embodiment of the invention the frequency of the thirdoscillation is a subharmonic or the frequency of one of the oscillationsw and 71w, the phase of the thirdoscillation being independent withrespect to the direction.

When using the method according to the invention there are obtained twoindications of the direction to be determined, one of which is a nbigucus and proportional to (71:1) [1, whereas the other determines theangle ,8 unequivocally. By these two indications, which reveal theaccurate position of the direction to be determined in a definite sectorand the spacial sector in question respectively, the direction to bedetermined is fixed unequivocally.

A special advantage of the method according to the invention consists inthat the purpose aimed at is attained with a minimum of additional meansin a beacon transmitter and receiver. This holds more particularly wherethe third oscillation is transmitted modulated on a carrier wave havingthe same frequency as the oscillations o and no, as is preferably thecase.

The relative position of the third oscillation and the two otheroscillations is preferably such that these oscillations pass at leastonce through zero simultaneously per cycle of the oscillation having afrequency w. By this adjustment one may be sure that those indications,6 and (iii-1H3 have direction of orientation in common.

In order that the invention may be clearly understood and readilycarried intov eifect it will now be described more fully with referenceto the accompanying drawing, given by way of example.

Inthe drawing, wherein like elements are referred to by like referencenumerals;

Fig. 1 is a schematic diagram of a preferred embodiment. of a beacontransmitter in accordance with the. invention,

Fig. 2 is the schematic diagram of a receiver for intercepting signalsof the type transmitted by the beacon shown in Fig. 1, and

Fig. 3 is the schematic diagram of a second It preferred embodiment of abeacon transmitter in accordance with the invention.

Fig. 1 represents diagrammatically a form of construction of a beacondevice which is suitable for carrying out the method according to-theinvention. In this beacon device a high-frequency oscillator l generateshigh frequenoy oscillations which, as the case may be, are suppliedthrough a frequency-multiplication device 2 and a high frequencyamplifie 3 to a final amplification stage 4 and two push-pull modulators5 andt, in both of which modulators the, h gh-fr qu y oscillations are Gmodulated with carrier-wave suppression by two oscillations havingfrequencies w and m], between which a harmonic relation exists, and by athird oscillation 2w whose frequency amounts to double the frequency ofone of the oscillations w and no. The modulat ing oscillation having afrequency w is generated by means of an oscillator l and supplied on theone hand to the modulator 5 through an amplifier and on the other handto the push-pull modulator 8 through a phase shifter 9 bringing about aphase displacement of 90 and an amplifier iii. By means of afrequency-amplification device ii the modulating oscillation having afrequency no is derived from oscillations gen- .erated by the oscillatorl and supplied on the one hand, through the low-frequency amplifier 8,to the ,modulator 5, and on the other hand through a phase-shifter l2and the low-frequency amplifier it to the modulator 6. The thirdmodulating oscillation having a frequency 2w is taken, by means of afrequency-multiplication device 13, from the oscillation generated bythe oscillator and supplied on the one hand, through the amplifier 8, tothe push-pull modulator 5, and on the other hand through a phase-shifterl4 and the amplifier it to the modulator.

In addition, the beacon device shown in Fig. 1 comprises four verticaldipole aerials l5, [6, ii and i8 which are placed in the angles ofdeviation of a square and extend normally to the plane of the drawing,an aerial it being placed at the centre of the square and extendingparallel with the other aerials.

The oscillations appearing in the output circuit of the power amplifier4 are supplied to the central aerial 59, whereas the oscillationsappearing in the output circuits of the modulators 5 and 6 are suppliedin phase-opposition to the aerials i5, I1 and i5, i3 respectivelylocated at the diagonal points of the square.

Consequently, in the aforesaid device the aerials placed at the anglesof deviation of the square are fed in such a manner that the phasedisplacement between the modulation of the modulated oscillationssupplied to every two neighbouring aerials is equal to the spacial angleof 90 between the two aerials. This results in that a high-frequencyfield, which is modulated by three oscillations w, 77.10 and Zr, isradiated in such a manner that the phase of each of the oscillationsobtained after detection is dependent with respect, to the direction.The phase shifters 9 and it are adjusted in such a manner that thecurrent in the antenna [3 for the two cillations w and 2w is leading andlagging respectively with respect to that in the remaining aerials, as aresult of which the phases of the modulations w and 2a: vary in the samesense with the direction.

By means of phase shifter 28 it can be achieved that the relativeposition of the three oscillations o), no and 2w obtained afterdetection is fixed in a definite direction (direction of orientation)and is preferably such that the three oscillations simultaneously passthrough zero at least once per cycle of the oscillation having afrequency 0:. Consequently, in any direction forming an angle ,8 withthe direction of orientation three oscillations are obtained afterdetection, one of which is proportional to Sil'l.(wifi), the second tosin.(nwtfl) and the third to sin.(2wt,8).

According to the invention the angle to be determined is derived bothfrom the oscillations sin (wt-/3 and SlI1.(1Lwt-fl) and from the0scil1ations SlI1.(wt-,B) and sin.(2wtp).

The oscillations sin.(wtfi) and sin.(nwtfi), as has been set out in theabove identified copending application, permit the angle to bedetermined to be derived by n-times frequencymultiplication of theoscillation having the lower frequency obtained after detection, whichyields an oscillation proportional to sin.(nwtnfi). By determining thephase angle between the frequency-multiplied oscillation and'theoscillation having the higher frequency obtained after detection, whichis proportional to Sll1.(7bwif3), a measuring characteristic is obtainedwhich is detcrmined by ("rzl) l3.

Similarly the oscillations proportional to sin. (wt-c) and sin. (Zeb-B)permit a measuring characteristic to be derived which is determined by(1zl)/3=p, since in this case 11:2.

Consequently, by a slight extension of transmitting apparatus, viz. byproviding the devices 43 and i l, the ambiguity of the accurateindication achieved by the transmission of the oscillations w and 1w iscompletely obviated, whereby the usefulness of the method set out in theabove mentioned patent application is materially increased.

A form of construction suitable for the reception of the oscillationstransmitted by means of a device as shown in Fig. l, is represented inFig. 2. In this device the modulated oscillations picked up by an aerial2B are supplied to a highfrequency amplifier 2! which is connected incascade with a mixing stage 22, an intermediatefrequency amplifier 23and a detector 24. The output circuit of the detector comprises threefilters 25, 26 and 2? that are tuned to the frequency w, the frequency1w and the frequency 2w respectively.

To derive the angle ,8 from the oscillations w and m: the oscillationshaving the lower frequency w are supplied to a phase meter 29 through afrequency-multiplication device 23, whereas the oscillations having thefrequency )Lw are directly supplied to a phase meter 29, the latterdetermining the phase angle (nl) 9 between the frequency-multipliedoscillation having the lower frequency and the oscillation having thehigher frequency m. In order to cure the ambiguity of the indicationthus obtained another phase meter 38 is provided to which theoscillation having a frequency 2w is directly supplied, and theoscillation having a frequency w is supplied through a frequencydoublingdevice 35. In the phase-meter 30 is determined the phase-angle s betweenthe oscillations supplied thereto having a frequency 20:. If desired,only one phasemeter may be used. In this case it is necessary to provideswitches by which either the output voltage of the frequency amplifier28 and of the filter 26 or the output voltage of the frequency doubler3! and of the filter 2? are simultaneously sup plied to the phase meter.

It stands to reason that for deriving a measuring characteristic, whichis determined by (n-Dp and 8 respectively, from the relative position ofthe oscillations having the frequencies or, no and 2w respectively,which are obtained in the receiver after detection, use may also be madeof a device other than that shown in Fig. 2.

The aforesaid receiving device is suitable not only for the reception ofthe oscillations transmitted by means of a device shown in Fig. 1 butlends itself, in principle, to the reception of all beacon devices thatmay be used for carrying out the method according to the invention, itbeing only necessary that the filters interposed in the output circuitof the detector 24 are tuned respectively to the three oscillationstransmitted by the beacon transmitter.

A receiving device according to the invention preferably comprisesautomatic gain control or a limiter so as to achieve an indication whichis independent of the amplitude of the oscillations to, no and 2:0.

If desired, as shown in Fig. 3, the third oscillation may also betransmitted with a frequencyindependent phase by the beacon transmitter;in this case the aerial l9 may be used for transmitting the thirdoscillation. The frequency of the third oscillation produced in devicel3 acting as a divider and fed to modulator l4 whose output is fed toaerial I 9 may then be a subharmonic of one of the oscillations in andlbw, the relative position of two oscillations with a frequencydependentand a frequency-independent phase respectively yielding a measuringcharacteristic which is an unequivocal measure of the angle if the phaseof the oscillation having frequencies harmonically related with thelower frequency is independent with respect to the direction.

What I claim is:

1. In a radio beacon, a transmitter comprising means foromnidirectionally propagating in space a carrier wave, and means forpropagating in space a suppressed carrier wave having first and secondmodulation components whose frequencies are difierent and harmonicallyrelated and a third modulation component whose frequency is a harmonicof one of said first and second components, each component having aspacephase depending on bearing.

2. In a radio beacon, a transmitter comprising a carrier wave source,first, second and third oscillatory modulation sources having difierentand harmonically related frequencies, a pair of balanced modulators,means to apply each of said first, second and third modulations in phasequadrature to said balanced modulators, means to apply said carrier Waveto said balanced modulators to combine with the modulations therein,said carrier wave being suppressed in said balanced modulators, firstantenna means coupled to said wave source for radiating said carrierwave omnidirectionally, second antenna means coupled to said balancedmodulators and disposed in predetermined relation to said first antennameans for radiating a rotating field constituted by said suppressedcarrier wave with said first, second and third modulations, thespace-phase of said modulations being a function of bearing.

3. An arrangement, as set forth in claim 2, wherein said second antennameans includes four radiating elements positioned at the corners of asquare, one of the balanced modulators being coupled to one pair ofdiagonally opposed elements for energizing said elements in oppositephase, the other of said balanced modulators being coupled to the otherpair of diagonally opposed elements for energizing said elements inopposite phase.

4. In a radio beacon, a transmitter comprising a carrier wave source, anoscillatory modulation source, a pair of balanced modulators each havingtwo inputs, means to apply said carrier'wave to one input of saidmodulators, a frequency multiplier coupled to said modulation source, afrequency doubler coupled to said modulation source, means for applyingin phase quadrature the original modulation from said modulation source,the multiplied modulation from said multiplier and the doubledmodulation from said doubler to the other input of said modulators, saidmodulators suppressing said carrier wave, first antenna means coupled tosaid carrier wave source for radiating said carrier waveomnidirectionally, and second antenna means coupled to said modulatorsand disposed in predetermined relation to said first antenna means forradiating a rotating field constituted by the suppressed carrier wavewith said first, second and third modulations.

5. A transmitter, as defined in claim 4, further including an adjustablephase shifter interposed between said modulation source and the otherinput of said modulators for effecting a predetermined phase relationbetween the original modulation and the multiplied and doubledmodulations.

6. In a radio beacon system wherein a carrier wave is transmitted aswell as a suppressed carrier wave with first, second and thirdmodulation components whose frequencies are harmonically related andwhose space-phase depends on bearing, a receiver for said wavescomprising means to detect said Waves to derive said modulationcomponents, filter means to separate said components, frequencymultiplying means coupled to said filter means for equating thefrequencies of said components, phase indicating means to compare saidfirst and second components, and phase indicating means to compare saidsecond and third components.

. FRANK DE FREMERY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,922,677 Greig et al. Aug. 15,1933 2,252,699 Byrne Aug. 19, 1941 2,253,958 Luck Aug. 26, 19412,394,157 Earp Feb. 5, 1946 2,422,110 Luck June 10, 1947 FOREIGN PATENTSNumber Country Date 385,521 Great Britain Dec. 29, 1932

